Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1986-11-19
1988-08-23
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356395, H01J 314
Patent
active
047663103
ABSTRACT:
A position measuring instrument, comprising a scanning grid, a scale grid and an illumination unit, is used to produce two sets of diffracted partial light rays. The scanning grid defines a grid constant and is formed by two scanning fields, constructed as phase grids, offset to one another in the measuring direction by 1/4 of the grid constant. The phase grids have a slat-to-furrow width ratio that deviates from a 1:1 ratio. The scale grid has the same grid constant as the scanning grid but has a slat-to-furrow ratio of 1:1. The grids cooperate with the illumination unit to produce diffracted partial light rays of several orders. An oppositely deflecting prism is allocated to each scanning field. A first and second set of diffracted partial light rays are generated, wherein the second set is opposite in phase to the first set. A photodetector is allocated to each respective selected order of the two sets of light rays to produce corresponding electrical signals.
REFERENCES:
patent: 3812352 (1974-05-01), MacGovern
patent: 4051367 (1977-09-01), Sayce
patent: 4176276 (1979-11-01), Kaul et al.
patent: 4461083 (1984-07-01), Ernst
patent: 4677293 (1987-06-01), Michel
Dr. Johannes Heidenhain GmbH
Nelms David C.
Ruoff Jessie
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